ANESTHESIA FOR LASER SURGERY

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ANESTHESIA FOR LASER SURGERY:

ANESTHESIA FOR LASER SURGERY Moderator: Dr. Sudarshan Presenter: Dr. Lokesh

PowerPoint Presentation:

Glossary of Laser Terminology Active medium A material that acts as a laser with the proper excitation Aiming beam A very low-powered laser beam that is collimated with the high-powered, often invisible therapeutic beam to illuminate the target site Attenuation The reduction in beam energy by absorption or scattering as it passes through matter Coherent light Light in which the photons all have the same wavelength and maintain a constant in-phase relationship with each other Continuous wave (CW) mode A mode of operation in which the laser discharge is continuous Collimation The property of a light beam that describes the degree to which the constituent photons move in a single direction; highly collimated beams do not spread in diameter as they move away from the source Dopant A chemical added to a crystal matrix to serve as an active laser constituent

PowerPoint Presentation:

Energy density The amount of energy per unit area arriving at a surface, usually expressed in joules per square centimeter Excimer Excited dimer; a type of laser based on the transition states of a diatomic molecule (e.g., ArF, KrF, XeCl); these lasers produce photons of very high energy Monochromatic light Light of a single wavelength or color Neodymium (Nd) A rare earth metal, frequently chosen as a laser material within a substrate of glass or yttrium-aluminum-garnet (YAG) Photon A quantum of electromagnetic energy possessing both wavelike and particle-like properties; photons travel at a constant speed of approximately 300 million m/sec Pulsed mode A mode of operation in which the laser delivers discrete (usually quite brief) bursts of photons Pump The means of including an electron population inversion so that stimulated emission may occur Resonator The combination of laser material and mirrors necessary to support laser activity

PowerPoint Presentation:

Spontaneous emission The emission of a photon when an excited orbital electron decays back to its ground-state energy Stimulated absorption The process by which an orbital electron captures the energy of a colliding photon and is boosted to a higher-energy orbital Stimulated emission The process by which an electron in a high-energy orbital, if struck by an appropriate photon, emits a new photon of wavelength, phase, and direction equal to those of the original, colliding photon Wavelength The distance from peak to peak of a photon wave; the usual units for light waves are nanometers (nm) or micrometers (µm)

PHYSICS OF LASER LIGHT:

PHYSICS OF LASER LIGHT Visual light is electromagnetic radiation, a spectrum from microwaves to gamma rays in increasing order of frequency. In 1864, Maxwell explained that light is an electromagnetic wave with combined electric and magnetic oscillations that propagates at 299,792,458 m/sec. Einstein- (Quantum mechanics)- He explained that all electromagnetic radiations contain photons Their properties are consistent with particles and waves. They propagate in a vacuum, without diminishing, at a constant speed of 299,792,458 m/sec. E=h γ 2.2998/ λ × 10 8 m/s= γ (Hz)

PowerPoint Presentation:

Photoelectric effect: Light of a certain color (e.g., blue) causes metal to eject electrons at a rate proportional to the brightness of the light, whereas intense light of other colors (e.g., red, orange, yellow) cannot. Photoelectric effect is independent of no. of photons. Only photons of higher energy (even it is single) can provide energy necessary to stimulate electron absorption.

PowerPoint Presentation:

Spontaneous emission: The emission of a photon when an excited orbital electron decays back to its ground-state energy Stimulated absorption: The process by which an orbital electron captures the energy of a colliding photon and is boosted to a higher-energy orbital Stimulated emission : The process by which an electron in a high-energy orbital, if struck by an appropriate photon, emits a new photon of wavelength, phase, and direction equal to those of the original, colliding photon Normally the tendency is towards spontaneous emission. But in circumstances called population inversion, in which electrons are pumped to higher orbital wall, waiting for photon to come along and start chain reaction of stimulated emission.

PowerPoint Presentation:

Laser differs from ordinary light in that: It is monochromatic– of well defined, very narrow wavelengths. Coherent: all of them oscillate synchronously. (in identical phase). Collimated: have minimal dispersion. so it generate intense and powerful beams– deliver intense energy to small targets.

PowerPoint Presentation:

Laser systems:

Laser systems::

Laser systems: Component Gas Solid Head Yes Yes Lasing medium Yes 1.Laser passive medium: YAG 2. Dopant : Nd, Ho Energy source Xenon flash lamp High voltage terminals Output Continuous or intermittent pulsed beam Pulsed beam

PowerPoint Presentation:

Lasers are inefficient in converting electricity to light. So, large power (>1000W AC) is required. It is converted to high voltage 5000-30,000V. So a coolant is used which may be running water, or a non-medical compressed gas. Frequency doublers: If a beam of light is passed through KTP- potassium titanium phosphate, the emerging light is a mixture of original wavelength and a light with wavelength half of the original light.

PowerPoint Presentation:

Heat resistant (sapphire) direct contact probes– for ‘no touch technique’ These probes require active cooling– compressed gas or liquid jet– contributed for morbidity and mortality. Mechanism of action: Thermal conversion – to surface heat (>800C) Transmission of infrared rays to surrounding tissue.

Clinical applications:

Clinical applications Allow highly precise microsurgery Can reach difficult to reach sites like: percutaneous diskectomy, endovascular angioplasty Produce intense heat. Approx 2500cal/s – precise rapid vaporization of tissues. Lasers don't increase the energy of photon but they place more photons at a given place and time than other light source. Laser surgeries are relatively ‘dry’ – near instantaneous sealing of blood vessels and lymphatics.

BIOLOGICAL EFFECTS:

BIOLOGICAL EFFECTS When an atom interacts with a photon whose energy doesn’t match a possible electron transition – atomic vibrations – heat. Long infrared wavelength: absorbed by water Powerful focused CO2 beams – explosive vaporization of tissues – little damage to underlying tissues. Excimer lasers: precise effect – UV rays – absorbed more intensely by water and other molecules Near infrared from Nd-YAG: diffuses through several millimeters More widely disseminated Less vaporization and more thermal coagulation. Nd-YAG or Holmium: replacing electrodessication for TURP. Reduced incidence of TURP syndrome because saline irrigant can be used. Office based resection of laryngeal pappilomatosis and dysplasia using topical local anesthesia Laser uvuloplasty for obstructive sleep apnea.

PowerPoint Presentation:

Ruby laser: absorbed potentially by cells containing dark pigment. Argon and Krypton – penetrate skin and ocular structures – absorbed by hemoglobin – coagulation. Excimer: UV rays – ionization – mutation and carcinogenesis. Very high energy per photon. Highly absorbed Extremely fine point of focus. Provide finely controlled vaporization and coagulation of cornea – for photorefractive surgeries – LASIK Other effects: Erbium laser – disrupt cutaneous diffusion barrier and increase delivery of topically applied drugs.

RISKS OF LASER:

RISKS OF LASER CONSIDERATIONS: Ignition is almost instantaneous Supply heat to a fuel source several cm away Skin under drapes may burn but drapes may not. Laser beams can be reflected from metallic surface igniting materials at a remote location.

PowerPoint Presentation:

Laser risk classification: Class I : leaser totally enclosed or with extremely less output. Class II : low risk – equivalent to staring sun – can cause central retinal injury. Not hazardous until one overcomes natural aversion to bright light. Class III : operate at power level >1mW IIIa – 1-5mW – moderate ocular hazard. IIIb – 5-500mW – potentially hazardous to eye. Class IV : any continuous wave or laser output >500mW pose serious risk to eye, skin. Also fire hazard.

PowerPoint Presentation:

Laser hazards: Atmospheric contamination Perforation of blood vessel or structure Embolism Inappropriate energy transfer

ATMOSPHERIC CONTAMINATION:

ATMOSPHERIC CONTAMINATION Vaporization – plume of smoke and fine particulates (0.1-0.8mcg, avg 0.3mcg) Deposited in alveoli. Leads to: Objectionable odor Headache, nausea Interstitial pneumonia, bronchiolitis reduced mucociliary clearance. Inflammation and emphysema. Laser plumes: Are mutagenic Acts as viral vector Prevention: Smoke evacuation at surgical site. Special highly efficient masks (Ord masks filter only up to 3 micrometer) Should be dry, changed periodically.

TISSUE VESSEEL PERFORATION:

TISSUE VESSEEL PERFORATION Misdirected laser perforate viscous or large vessel laser induced pneumothorax. Nd-YAG depth of damage is unpredictable Bleeding and perforation don’t manifest for several days post op until edema and necrosis have become maximal.

PowerPoint Presentation:

EMBOLISM Nd-YAG– venous air embolism Particularly with hysteroscopic surgery. Coolant from sapphire probe leak– fill– embolus. So, liquid coolant preferred (saline) Uterine distension with saline – fluid overload similar to TURP is possible. Resection of tumors in trachea.

ENERGY TRANSFER TO INAPPROPRIATE LOCATION:

ENERGY TRANSFER TO INAPPROPRIATE LOCATION Medical lasers are transmitted transparently through air Reflected by smooth metal surface.

EYE PROTECTION:

EYE PROTECTION CO2 laser – corneal injury. Argon, Krypton, Nd-YAG, Ruby – retinal injury. For the patient: Lids are taped closed and covered with saline soaked knit or metal shield. For OT personnel: Protective goggles specific for laser wavelength (including side cover). For CO2 laser, any clear glass or plastic surface is sufficient. Regular glasses may be sufficient but not contact glasses. Nd-YAG – Green tinted goggles Argon-Krypton – Amber orange filter KTP Nd-YAG – Red filter All windows covered and warning signs put.

ET TUBE FIRES:

ET TUBE FIRES Incidence -0.5-1.5% Laser induced ignition of ET tube is responsible for most of the perioperative complications. Fire can be due to: Direct effect Reflected laser light Incandescent tissue particles blown out Initially fire to external surface – local destruction Progress– interior of tube – oxygen enriched gas to and fro flow– blowtorch like flame. Blowing of particles down to pulmonary parenchyma. Puncture or unrecognized deflation of tube cuff – oxygen enriched gas– fire.

PowerPoint Presentation:

Modalities to prevent airway fire: Reduce flammability of ET tube Reduce available oxygen consumption Removal of flammable materials from airway.

PowerPoint Presentation:

All ET tubes are flammable. PVC tubes: most widely used – ignite very easily by CO2 lasers Transparent and immune to Nd-YAG in vitro but a coat of blood or mucus absorb energy and restore hazard. Produce widespread deposit of carbonaceous debris and ulceration and inflammation. Red rubber: more resistant to ignition Less debris and inflammation. Silicone tubes: Most resistant Produce copious white silica ash – silicosis. Addition of 2% halothane vapor retards ignition. Many physicians recommend red rubber ET tubes.

Protection of ETT:

Protection of ETT Extrinsic protection: Muslin– inflammable if dry. Dental acrylic– makes tube rigid with rough surface– trauma. Wrapping: Tapes used: Aluminum – CO2 and KTP not Nd-YAG. Copper CO2, KTP, Nd-YAG. Plastic tapes with metal and adhesive on opposite sides – only for CO2.

PowerPoint Presentation:

Method of applying protective foil: Clean with alcohol- cut one end of tape to 60 deg- align to proximal end of cuff-tube junction- wrapped in spiral with 30 deg overlap. Wrinkles are to be eliminated with no areas of exposed tubing or adhesive.

PowerPoint Presentation:

Disadvantages: No FDA approval No cuff protection Adds to thickness of the tube Protection varies with type of metal foil. Adhesive backing may ignite if exposed. May reflect laser to non-target tissues Rough ends may damage mucosal surfaces.

Laser resistant tubes:

Laser resistant tubes Even though claimed to be laser resistant, they are not completely laser proof. May catch fire if laser power too high or for too long.

Laser shield tube:

Laser shield tube Silicone with aluminum wrap and outer Teflon coat. Outer Teflon coat may be vaporized. Exposure of unprotected parts Methylene blue crystals- obstruct pilot tube

Laser flex tubes:

Laser flex tubes Stainless steel tube with smooth plastic surface and matte finish 2 cuffs Cuff and tip vulnerable Stiff and rough surface More time for intubations and extubation Large diameter Not fit to Bullard scope

Sheridan laser tracheal tube:

Sheridan laser tracheal tube Red rubber tube wrapped with copper foil tape Thick wall High pressure cuff

Norton tubes:

Norton tubes Reusable flexible spiral wound metallic tube with stainless steel connector and thick walls. Flexible coils not air tight. Rough surface Twist on stylet No cuff.

Bivona foam cuff tube:

Bivona foam cuff tube Aluminum and silicone spiral with silicone covering Self inflating cuff Poorly resistant to all lasers More sore throat Cant be deflated if punctured.

lasertubus:

lasertubus White rubber with merocel sponge cuff within cuff Resistant to Ar, Nd-YAG, CO2 lasers Bending above sponge cover- kinking.

Protection of ET cuff:

Protection of ET cuff High volume low pressure cuff more vulnerable to misdirected laser. Although combustion possible, simple puncture more common. Recommended: Fill cuff with saline +Methylene blue. Place cuff as distally to trachea as possible. Completely cover cuff with moistened cotton pledgets.

PowerPoint Presentation:

Modalities to prevent airway fire: Reduce flammability of ET tube Reduce available oxygen consumption Removal of flammable materials from airway.

PowerPoint Presentation:

Reduce FiO2 to minimum consistent with patient oxygenation (FiO2 ~0.4) Diluents: Air Helium Nitrous oxide not to be used as it supports combustion Volatile anesthetics: Non-flammable at clinically relevant concentrations. Undergo pyrolysis during fire to form potentially toxic compounds. They are not recommended. oxygen can collect beneath drapes above skin– use adhesive drapes or use suction.

Other measures:

Other measures ETT of a smaller diameter to be used. Tubes to be fixed such that they can be removed rapidly in case of fire. Fastest way to deflate a fluid filled cuff is to remove contents with syringe rather than cutting the pilot balloon. If the cuff deflates suddenly during procedure, oxygen flush should not be used. Use fire/laser resistant drapes. Laser resistant circuit protectors. Remove disposable paper wrappers or covers before start of case.

PowerPoint Presentation:

Modalities to prevent airway fire: Reduce flammability of ET tube Reduce available oxygen consumption Removal of flammable materials from airway.

JET VENTILATION:

JET VENTILATION Based on Bernoulli’s principle: to augment ventilation produced by narrow high speed gas stream in venturi tube. Jet ventilation: intermittent high pressure oxygen supply directed at glottis through a small metal tube – ventilating bronchoscope or a 12G blunt needle. Most suitable for benign glottic pathology and early malignancy where airway obstruction is not anticipated.

PowerPoint Presentation:

Types: Supraglottic : describes a technique in which a jet of gas emerges in the supragloiits by attachment of a jetting needle to rigid surgical suspension laryngoscope. Clear unobstructed view for surgeon with no risk of airway fire. Limitations: Misalignment of laryngoscope to laryngeal inlet – poor ventilation and gastric distension. Blood, smoke, debris blown down to trachea. Considerable vibration and movement of vocal cord– require ventilation to be stopped while operating. Inability to monitor EtCO2. Risk of barotrauma with pneumomediastinum, pneumothorax, subcutaneous emphysema.

PowerPoint Presentation:

Subglottic : Allows delivery of a jet of gas directly into trachea by placement of a small catheter through the glottis into trachea. More efficient than supraglottic Reduced driving pressure, minimal vocal cord movement, good surgical field. No time constraints on the surgeon in placement of rigid scope. Disadv: laser induced airway fire.

PowerPoint Presentation:

Tran tracheal jet ventilation: Elective Tran tracheal catheter placed by piercing trachea or cricothyroid membrane under LA. Carry great risk of barotrauma. Risk of blockade, kinking, infection, bleeding, failure to site catheter. Use of this method requires careful evaluation of potential risks and benefits. Procedure of insertion: Preoxygenation, induction, muscle relaxant, laryngoscopy, topical lidocaine around VC LMA with 100% oxygen till surgeon is ready to site rigid scope with jetting needle. Alternatively facemask must be ready. Maintained with propofol, alfentanyl or remifentanyl IV In the end again LMA inserted and reversed for smooth emergence.

PowerPoint Presentation:

Monitoring : Observe chest movements, SaO2 Listening to change in sound during air entry or exhalation. Disadvantages: Patients may absorb CO from smoke– overestimate saturation Barotrauma, pneumothorax. Use of only IV agents. Gastric distension Relative requirement of compliant lungs. Distal seeding of virus in papillomas.

PowerPoint Presentation:

Other modalities: Spontaneous ventilation with apnea– with GA by nasal insufflation or bronchoscopic delivery of potent inhaled anesthetic. GA with hyperventilation followed by extubation for 90-120 sec– hypoxia monitored by pulse oximetry.

AIRWAY FIRE PROTOCOL:

AIRWAY FIRE PROTOCOL Remove source of fire quickly Stop ventilation and remove tracheal tube Submerge tube in water Ventilate with facemask and reintubate. Assess airway damage with bronchoscopy, serial CXR, ABG Consider bronchial lavage, steroids.

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